1. Field of the Invention
The present invention concerns a corrosion resistant Ti based alloy and, more particularly, it relates to a corrosion resistant Ti based alloy of excellent corrosion resistance, as well as workability and crevice corrosion resistance.
2. Description of the Prior Art
Heretofore, Ti has been well-known as a metal of excellent resistance and used generally as an industrial structural material such as chemical plants, but there is a room for doubt about the corrosion resistance depending on the circumstances in which it is used.
Ti shows excellent corrosion resistance in an oxidative corrosive circumstance such as of nitric acid and in corrosive circumstance containing sea water and like other chlorides. However, in a non-oxidative circumstance such as hydrochloric acid and sulfuric acid, it does not show so excellent corrosion resistance as in the oxidative circumstance as described above.
Further, in a circumstance containing, for example, a chloride solution at high temperature it has been well-known that, if crevices are present in the material put under the circumstance, Ti in the crevices locally suffers from corrosion.
For resolving such problems when Ti is put to a readily corrosive circumstance, corrosion resistant Ti based alloys incorporating various alloying elements to Ti have already been proposed and commercially available.
Then, as the Ti alloys, there can be mentioned such alloys as Ti--Pd alloy and Ti--Ni--Mo alloy. However, Ti--Pd alloy involves an economical problem since Pd is expensive and Ti--Ni--Mo alloy has a problem of poor workability and it has not been used generally although it is excellent in the corrosion resistance.
Accordingly, the present inventors, taking notice of the problems in the Ti alloys which are said to have satisfactory corrosion resistance in the prior art, have already proposed Ti alloys which show excellent corrosion resistance in the non-oxidative circumstance and, further, can satisfy crevice corrosion resistance in such circumstance as in the chloride solution at high temperature in view of the practical use in Japanese Patent Application Hei 02-069066 and 02-283755, and have developed a Ti alloy incorporated with Ag or Au to a group of Ni, Pd or Ru.
However, the Ti based alloy exhibits excellent performance in the corrosion resistance which is an object of the corrosion resistant Ti based alloy according to the present invention but Ag, etc. incorporated in a melting device for the Ti based alloy gives loss by evaporation, making it difficult to conduct alloy casting at a good yield.